1. Field of the Invention
The present invention relates to an image pickup element such as a complementary metal oxide semiconductor (CMOS) image sensor and a method for controlling the image pickup element, and a camera.
2. Description of the Related Art
In recent years, in CMOS image sensors, the number of pixels has been increased, and the light-receiving area has been increased. In a typical X-Y address CMOS image sensor, a plurality of pixel circuits are arranged in a matrix form in a pixel unit. The pixel circuits are divided into groups so that each of the groups is provided in a corresponding one of columns, and the individual pixel circuits in each of the groups are connected to a corresponding one of vertical signal lines.
A parasitic resistance and a parasitic capacitance exist in each of the vertical signal lines. Accordingly, when the values of the parasitic resistance and the parasitic capacitance are large, the pixel readout time is increased. As a result, shifts between the pixel readout times for the individual columns or shifts between the charge accumulation times occur, and a focal plane phenomenon easily occurs. The focal plane phenomenon is a phenomenon in which distortion occurs in a picked-up image, and it is difficult to correct the distortion in a picked-up image using affine transformation or the like.
In order to reduce the phenomenon, a design in which the parasitic resistances are reduced by increasing the width of the vertical signal lines, and a design in which the parasitic capacitances are reduced by increasing the wiring pitch of the vertical signal lines have been performed. A design can also be performed, in which the parasitic resistances and the parasitic capacitances of the vertical signal lines can be reduced by chaining the pitch of the pixel circuits. However, the design has a disadvantage that the characteristics of pixels are sacrificed.
For this reason, a CMOS image sensors are is proposed, in which the parasitic resistances and the parasitic capacitances of vertical signal lines are reduced by dividing a pixel region into two regions, and by electrically disconnecting the vertical signal lines from one another in the pixel region.
The CMOS image sensor may be referred to as a “sense-amplifier-type CMOS image sensor”. Charge that is accumulated in pixel circuits is output as voltage signals to the vertical signal lines without being amplified, and sense amplifiers read changes in levels of the voltage signals that are transmitted to the vertical signal lines.